Class 83 Monday 6/12/23

Warm Up: 

2.  What are RGB and CMYK color models?  What's the difference?

Today: 

  • Quiz retake

  • Final exam review

  • Course Evaluation

  • Is there anything else you want to know about physics that we haven't already covered?

Homework:  
  • Prepare for final exam

Class 82.5 Friday 6/6/23

Warm Up: 

The index of refraction (n) of a substance varies with the wavelength of the waves passing through the substance.  This phenomenon causes dispersion, which is the separation during refraction of light rays of different color. 

 

1.  What are the colors of visible light, in order of wavelength?

2.  If n decreases with increasing wavelength, where will the different colors emerge from this prism?

 

Scattering is the phenomenon whereby light "bounces off" of particles (e.g. N2 molecules, ice crystals, and smoke) in the sky.  Shorter wavelengths of light are more susceptible to scattering than longer wavelengths.

2.  Why is the sky blue?

3.  Why are sunsets red?

 

 

Today: 

  • Return Quizzes

  • ??

Homework:  
  • Quiz retake on Monday
  • Prepare for final exam

Class 82 Thursday 6/8/23

Warm Up: 

Fred is conducting a laser experiment on a very, very, very fast train.  He attaches a mirror to the roof of the train car and shines a quick pulse of laser light directly upward at the mirror.  Hank is standing still outside the train.  The train car is made of glass, so Hank can see the whole thing.

The pulse of laser light goes up, reflects off of the mirror, and then goes back down to the floor.  There's enough dust in the air to make the laser pulse visible.

1)  If Fred and Hank were to draw the laser pulse's "flight path" (as each of them sees it), what would each of them draw?

2)  Who would see light travel a greater distance?

3)  Assuming that the speed of the laser light is the same for both observers, who sees it travel for the longest amount of time?

Today: 

  • Quiz -- does anyone need time to prepare?

  • Rotational Motion Jeopardy!

Homework:  
  • Quiz retake on Monday
  • Prepare for final exam

Image result for nearsightedClass 81.5 Wednesday 6/7/23

Warm Up: 

1.  Why can't humans see clearly under water?

2.  Guess which condition (on the right) makes it easier to see clearly under water?  How does this relate to seals?

3.  Goggles and masks can be used to see clearly under water, but they distort the observed heights of objects.  Do they magnify or reduce?  Why?

Image result for diving mask

Today: 

  • Sorry, I haven't graded the retakes.  I should have them graded by tomorrow.

  • Check homework

  • Rotational Motion Jeopardy!

Homework:  
  • Quiz tomorrow, like the practice quiz  (Practice Quiz (p. 12) Solutions)

Class 81 Tuesday 6/6/23

Warm Up: 

None

Today: 

  • Sound/Waves test retake

Homework:  

Image result for optic nerve blind spotClass 80.5 Monday 6/5/23

Warm Up: 

1.  What would you guess is the approximate focal length of the human eye?

2.  Does that focal length change?  Explain.

3.  Why do we have a blind spot?

4.  How can you "find" your blind spot?

 

Today: 

  • Check/review homework

  • Discuss Final Exam

Homework:  

Class 80 Friday 6/2/23

Warm Up: 

Use your phone, a lens, and some paper to make an image, as shown on the right.

 

Today: 

Homework:  
  • Complete the lens equation problems on p.10-11. answers  After the first couple, feel free to create a spreadsheet.

Class 79.5 Thursday 6/1/23

Warm Up: 

1.  Why can't the observer see the penny? (and why can't you see the fish in the tank?)

2.  How can we make the penny or the fish visible by adding just one component to the system?

 

Today: 

Homework:  
  • None

Class 79 Wednesday 5/31/23

Warm Up:  Where does the fish appear to be located (in the eyes of the spearfisher)?

 

Today: 

Homework:  
  • Practice problems (#1-17, but many have been deleted) on p. 4-5 of handout Solutions

Class 78.5 Tuesday 5/30/23

Warm Up: 

The diagram below shows top views of the same boy looking into mirrors.  On the right, the mirror is a simple flat mirror.  On the left, the mirror is two separate mirrors arranged at right angles.  The boy has one blue eye and one green eye.

When he looks in the mirrors, where will his blue eye appear to be?  Why?

 

Today: 

Homework:  
  • None.  Enjoy your weekend!

Class 78 Friday 5/26/23

Warm Up:  None

Today: 

  • Test -- waves and sound

Homework:  
  • None.  Enjoy your weekend!

Class 77.5 Thursday 5/25/23

Warm Up: 

1. What were the loudest sounds ever (according to listverse)?

2. How is sound volume measured?

3.  Why is there a theoretical limit on how loud a sound can be?

Source of sound (in air) Sound Pressure -- amplitude
(psi) 		 Volume in Decibels, calculated by
20*LogP/Po		 Po (threshold of hearing, in psi) Loudest divided by Quietest
Shockwave (distorted sound waves > 1 atm; waveform valleys are clipped at zero pressure) 14.69543147 194.0956869 2.9E-09 5,067,390,163
Theoretical limit for undistorted sound at 1 atmosphere environmental pressure 14.69543147 194.0956869    
Stun grenades 2.900652647 180.0019545    
Simple open-ended thermoacoustic device[6] 1.830166788 176.0018534    
.30-06 rifle being fired 1 m to shooter's side 1.053662074 171.206067    
M1 Garand rifle being fired at 1 m 0.728498912 168.0006182    
Rocket launch equipment acoustic tests 0.580130529 166.0225545    
Jet engine at 30 m 0.091660624 149.9956962    
Threshold of pain 0.009166062 129.9956962    
Vuvuzela horn at 1 m 0.002900653 120.0019545    
Hearing damage (possible) 0.002900653 120.0019545    
Jet engine at 100 m 0.029006526 140.0019545    
Non-electric chainsaw at 1 m 0.000913706 109.9681656    
Jack hammer at 1 m 0.000290065 100.0019545    
Traffic on a busy roadway at 10 m 9.15156E-05 89.98194182    
Hearing damage (over long-term exposure, need not be continuous) 5.16316E-05 85.01035459    
Passenger car at 10 m 2.90065E-05 80.00195455    
EPA-identified maximum to protect against hearing loss and other disruptive effects from noise, such as sleep disturbance, stress, learning detriment, etc.   #NUM!    
Handheld electric mixer 5.51124E-06 65.57702656 Classroom Unit Ventilator  
TV (set at home level) at 1 m 2.90065E-06 60.00195455    
Normal conversation at 1 m 2.90065E-06 60.00195455    
Very calm room 9.19507E-08 30.02313979    
Light leaf rustling, calm breathing 9.16606E-09 9.995696197    
Auditory threshold at 1 kHz 2.90065E-09 0.001954545    

Today: 

  • Check/review homework

  • Test review -- test tomorrow

  • We haven't seen the ruffed grouse.  What else... Mechanical Waves Links

Homework:  
  • Test tomorrow

Class 77 Wednesday 5/24/23

Warm Up:  What is going on in this video?  Explain the physics.

Today: 

Homework:  

Class 76.5 Tuesday 5/23/23

Warm Up: 

If you're standing next to a race track, what do you hear as the cars pass you?

a.  The cars' pitches change from high to low.

b.  The cars' pitches change from low to high.

c.  There is no change in pitch

Today: 

  • Return retakes

  • Check/review homework (lab and problems)

  • Notes: Doppler Effect, packet p.11  Filled-In Notes

Homework:  

Class 76 Monday 5/22/23

Warm Up: 

None

Today: 

  • Test retake

  • Test on Friday -- 10 minutes shorter than usual, due to the "Hullabaloo."

Homework:  

Class 75.5 Friday 5/19/23

Warm Up: 

What is going on here?  What waves concepts can you spot in this "wave pool video?" 

Today: 

  • Check/review homework

  • Finish the lab

Homework:  

Class 75 Thursday 5/18/23

Warm Up: 

1.  What do the terms resonance and forced vibration mean?

2.  Which term applies to the body of a string instrument amplifying the string's sounds?

3.  Which term applies to breaking glass with sound waves? 

Today: 

  • Check/review homework

  • Resonance lab, pages 9-10

Homework:  

Class 74.5 Wednesday 5/17/23

Warm Up:  Assuming that the string on the right has a length of 1m, and also assuming that tension is kept constant...

1.  How many nodes and antinodes are pictured?

2.  Does this picture represent the fundamental frequency?  If not, what is the fundamental frequency?

3.  What is the speed of the waves that are traveling along the string?

4.  What wavelengths and frequencies can produce standing waves in this string?

5.  Why is it important that the tension is kept constant?

Today: 

  • Check/review homework

Homework:  
  • Practice:  #5 and 6 on p. 8 of the packet.  Solutions

Class 74 Tuesday 5/16/23

Warm Up:  What's happening in the "Amazing Water and Sound Experiment?"

Today: 

Homework:  
  • Practice:  #1-4 on p 7-8 of the packet.  Solutions

Class 73.5 Monday 5/15/23

Warm Up:  How does a speaker work?

Today: 

Homework:  

Class 73 Friday 5/12/23

Warm Up:  None

Today: 

  • Test

Homework:  
  • None

Class 72.5 Thursday 5/11/23

Warm Up:  The pickle, again.  Why does it light up on just one end? 

Let's assume that the salty, juicy, pickle has an initial resistance of 8 ohms.  What happens when current first begins to flow?  Why does light appear?  How does that change resistance?  What does that do to power?

 

Today: 

Homework:  
  • Study

Class 72 Wednesday 5/10/23

Warm Up:  Suppose you wired the bulb and the table saw (see photos) on the same circuit in your house.

1.  What would happen if you wired them in series?

2.  What would happen if you wired them in parallel?

3.  What would happen if you kept adding more of them to the circuit (in series or in parallel)?

4.  Does this fit well with the water and delivery truck analogies?

 

Today: 

  • Check/review the homework

  • Review the lab -- hand out markings then turn them back in.

  • Test on Friday over circuits and current

  • Start the new unit -- Get the first part of the Unit 11 Handout PDF

  • Mechanical Waves Links

Homework:  
  • None.  Test prep.

Class 71.5 Tuesday 5/9/23

Warm Up: 

Suppose you wire a circuit with the two bulbs, the battery on the right, wires of negligible resistance, and no other resistors.  Depending on how you set up the circuit, either bulb could burn brighter.

1. How could you wire the bulbs so that both of the bulbs light up the 10 ohm bulb burns brighter?

2. How could you wire the bulbs so that both of the bulbs light up the 1 ohm bulb burns brighter?

3.  Which scenario would produce the brightest bulb?  Which bulb would it be?

4.  Which scenario would produce the dimmest bulb?  Which bulb would it be?

 

Today: 

  • Check/review the homework

  • Review the lab -- hand out markings then turn them back in.

  • Test on Friday over circuits and current

  • Work time

Homework:  

Class 71 Monday 5/8/23

Warm Up: 

The figure on the right clarifies a formula that can be used for calculating the resistance (R) of a wire.  Can you figure out what it means and how it makes sense?

table of resistivities

Today: 

Homework:  

Class 70.5 Friday 5/5/23

Warm Up:  Deriving Kirchoff's Rules

1.  If you were to swim around the circuit, from point C to D to B to A, and back to C, what total change in potential (V) would you experience?  When would you gain potential (V)?  When would you lose it?  How much would you gain/lose?  What if you "traversed" loop C,D,B?  What would happen if you went the other way (B,D,C)?

2.  A "junction" is a point where multiple currents join into one, or where one current splits into multiple currents.  How many junctions are there in this circuit?  At these junctions, how does the amount of current entering the junction compare to the amount of current exiting the junction?

Today: 

Homework:  

  •  Complete the next two Kirchoff's Rules problems.  Solutions 

Class 70 Thursday 5/4/23

Warm Up: 

Assuming that the wires on the right have zero resistance...

1.  What is the resistance of the entire circuit?

2.  How much current flows through the resistor on the far right?

Today: 

  • Check homework.  Share puzzles.  Do a tricky one together.

  • Finish the Circuit lab  (PDF)

  • Start on the homework.

Homework:  

Class 69.5 Wednesday 5/3/23

Warm Up:  The graph on the right was made by providing a variety of voltages to a light bulb, and then measuring the current flowing through the bulb. 

1.  The graph is curved.  What does that tell us?

2.  What implication(s) does this have for the circuit lab?

3.  In the circuit lab, how could you find the resistance of an individual bulb?

Today: 

Homework:  

  • Create a complex circuit puzzle, like this one .  The puzzle goal is to find V, I, R, and P for the voltage source and for each of the resistors. To keep this from being too complicated, include only four resistors in your circuit, at least two of which are in parallel, and at least two of which are in series.  Try to provide just barely enough information in the chart for someone to be able to find the rest of the values.  Solve your puzzle on separate paper, so that someone else can try the puzzle in class tomorrow.

Class 69 Tuesday 5/2/23

Warm Up:  Can you anticipate what comes next in Mr. Chase's energy distribution analogy for circuits?

Today: 

Homework:  

Class 68.5 Monday 5/1/23

Warm Up:  Circuits Refresher
1.  What are voltage, current, and resistance?  What are their units?  What are their source units?

2.  What are the relationships between individual and total voltages, currents, and resistances in parallel and series circuits?

3.  Remember that Power = Work/Time.  Power can be thought of as the rate of energy use.  Its units are J/s, but we use Watts (W).  What is the formula for power, in terms of current and voltage?

4.  What are the relationships between individual and total power consumptions in parallel and series circuits?

 

Today: 

Homework:  

Class 68 Friday 4/21/23

Warm Up: None

 

Today: 

  • Optional Test Retake

Homework:  

  • None

Class 67.5 Thursday 4/20/23

Warm Up: Deriving the parallel circuit equivalent resistance formula...
1.  If the voltage provided by the battery is V, what is the total current flowing through this circuit with resistors having resistances equal to R1, R2, and R3?

2.  Use that total circuit current to calculate the overall (equivalent) resistance of the circuit.

 

Today: 

Homework:  

  • None.  Optional test retake tomorrow.

Class 67 Wednesday 4/19/23

Warm Up:  Where do "Circuit Reduction" rules come from?.  Use Ohm's law (I=V/R), common sense, and the water analogy.

1.  What does "circuit reduction" mean?

2.  If a car specifies "36psi (cold)" in the front tires, how much pressure is in the front tires when they are properly inflated and cold?  How does this relate to voltage?  What does V really mean?

3.  In the top diagram, what fraction of the total current (I), travels through point A?  B?  C?

4.  What are the pressures at locations A-C, in the top diagram?

5.  What are the pressures at locations D-J in the bottom diagram?

6.  In the bottom diagram, what fraction of the total current flows through each of the resistors?

7.  If the resistance of each resistor is 1 Ohm, what are the equivalent resistances of each circuit?

Today: 

  • Check/review homework

Homework:  

None

Class 66.5 Tuesday 4/18/23

Warm Up:  Check out the active graphic DC Circuit Water Analogy at Hyperphysics.com.  According to the analogy...

1.  Voltage is like _____

2.  Current is like _____

3.  Resistance (R) is like _____

 

Today: 

Homework:  

Class 66 Monday 4/17/23

Warm Up:  None

Today:    Test

Homework:  
  • None
    •

Class 65.5 Friday 4/14/23

Warm Up:  On Monday's test, when you have to charge a conductor, you may have more success if you use some of the electrophorus parts. 

1.  How could that work?

2.  Why might the electrophorus work better than the other methods we used?

3.  I have decided that it doesn't matter if, in the process of charging the conductor, you touch the conductor with foam, fabric, or acrylic.  Why does this not really matter?

 

Today: 

  • Check/review homework

  • Test review:

    • "4 minute drill"  Drill solutions

    • Formulas you may need:  You will be given qe, k, and the values of various metric prefixes.

    • Some suggestions for a problem-solving algorithm. Video explanation

    • Armed only with styrofoam and wool, be able to induce a specified charge (+ or -) on a conductor, with or without using yourself as an electrical ground.

Homework:  
  • Study
    •

Class 65 Thursday 4/13/23

Warm Up: 

The deceptively complicated case of the electrified pickle...

Why does the pickle light up?  Why does it light up on just one end?  Is it always the same end?

 

Today: 

  • Check/review homework

  • Notes: 18.7 -- Conductors and Fields in Static Equilibrium (packet p. 17-18). 

  • Work on practice test and practice the practical problem.

  • Test review tomorrow.  Test on Monday.

    •

     

Homework:  

Class 64.5 Wednesday 4/12/23

Warm Up: 

Of which of the following statements can we be most certain?

A)  The balloons have the same net charge

B)  The cat and the foam "peanuts" have opposite net charges.

C)  Both A and B are correct.

D)  None of these answers is (are) correct.

 

 

Today: 

  • Check/review homework

  • Go over tape answers

    • Some more tape questions...

      • Suppose you have a stack of three tapes, stuck to a table. 

        • How can you remove them so that two become positive and one becomes negative? 

        • How can you remove them so that one becomes positive and two become negative?

      • What is the charge of tape that's still on the dispenser?

      • What's the charge of a never-used tape roll, right out of the box?

       

  • Work time

Homework:  

Class 64 Tuesday 4/11/23

Warm Up:  Electric and Gravitational Fields -- In the equations on the right...
1.  What are the units of q?

2.  What are the units of E?

3.  What are the units of F?

4.  What are the units of g?  What other units would make sense?

5  How are g and E similar?

6.  How are g and E different?

 

Today: 

Homework:  

Class 63.5 Monday 4/10/23

Warm Up:  What's going to happen at the moment that this Van de Graaff Generator is turned on?  Why? 

Today: 

  • Check/review homework

  • Return retakes

  • Finish the clear tape tomorrow :-)

  • Electric Field:  Skip the mathematical aspect of electric field for now, and jump right into electric field lines.

     activity

Homework:  

Class 63 Friday 4/7/23

Warm Up:  None

Today: 

  • Disassemble your car.  Clean all of the axles, bearings, and nail heads, and return them to their storage locations.

  • Optional test retake -- rotational motion

Homework:  

  

Class 62.5 Thursday 4/6/23

Warm Up:  How can you approach and touch a working VDG without getting painfully shocked? 

Today: 

Homework:  

Class 62 Wednesday 4/5/23

Warm Up: 

1.  How does a Van de Graaff Generator Work?

2.  What can we do with a pith ball coated in conductive paint, suspended on a string next to the VDG?

Today: 

Homework:  

Class 61.5 Tuesday 4/4/23

Warm Up: 

The electrophorus is charged by rubbing a cat(fur) against the top of an insulating plate (I).  Next the conducting plate (C) is placed on top of the insulating plate.  Finally, the conducting plate is touched by the scientist.  Assuming that the cat fur has a strong affinity for positive charge...

1.  What is the charge of the plate before it is touched by the scientist? 

2.  What is the charge of the plate after it is touched by the scientist? 

3.  The scientist serves as an electrical ground in this demonstration.  What doest that mean?

Today: 

Homework:  

  •  None

Class 61 Monday 4/3/23

Warm Up: 

1.  If you rub a balloon on your head and then hold it next to your hair, your hair is attracted to the balloon.  Why? Triboelectric Series

2.  Your hair may also stand on end after being rubbed by a balloon.  Why?

Today: 

  • Return tests -- Optional retake is on Friday (end of the quarter)

  • Get the new handout -- Unit 8: Electric Charge and Electric Field  (PDF)

  • Rubber Band Car Contest -- Data collection and scoring spreadsheet

    • Tell me your estimated top speed and acceleration distance (distance until string comes loose)

    • Assign a random order

    • Warm-up.  10 minutes of practice time.  Do whatever you want to prepare for your turn.

    • Await testing -- no more practice

    • Testing -- If you don't like your first run, you can choose to have me delete the video and let you try a second time.

Homework:  

Class 60.5 Friday 3/31/23

Warm Up:  None

Today: 

  • Enter your car data and calculations into the spreadsheet provided in Google Classroom.

  • Make sure that your car is ready for the contest on Monday.

Homework:  

  •  Finish anything related to the car project.

Class 60 Thursday 3/30/23

Warm Up:  None

Today: 

  • Test -- Rotational Motion

  • Make a note at the top of your test if you did not use the formula sheet.

  • If you need the formulas, print these (PDF).

Homework:  

  •  None.  But maybe think about whether you have anything else to do to finish the car project.

Class 59.5 Wednesday 3/29/23

Warm Up:  None

Today: 

  • Review for the test:
    • Read through the test format, below.
    • Try the 4 minute drill.  Then check your answers here:  Answers
    • Study alone or in groups.
  • Test Format:
    • 15 Multiple Choice (1 point each) -- study the notes
    • 5 problems (30 points total)
      • Apply various angular kinematics formulas
      • Convert between angular and linear units
      • Torque
      • Rotational Version of Newton's 2nd Law
      • Angular Momentum
      • Conservation of Angular Momentum
      • Conservation of Energy with rotational and translational energy
      • Torque balancing by locating a fulcrum
  • Formulas offered during the test:  Word Document (PDF).

 

Homework:  

  •  The test is on Thursday.  Do whatever you need to do to pace yourself and be ready by then.

Class 59 Tuesday 3/28/23

Warm Up:  None

Today: 

Homework:  

  •   The test is on Thursday.  Do whatever you need to do to pace yourself and be ready by then.

Class 58.5 Monday 3/27/23

Warm Up: 

Today: 

Homework:  

  •  The test is on Thursday.  Do whatever you need to do to pace yourself and be ready by then.

Class 58 Thursday 3/23/23

Warm Up: 

1.  Why are you not allowed to perform an actual road test with your car? (by winding it up, setting it on the floor, and letting it go)

2.  What should you do if you don't trust your results in step 7 of the analysis (where you measure motor energy output)?

Today: 

Homework:  

Class 57.5 Wednesday 3/22/23

Warm Up: 

None

Today: 

Homework:  

Class 57 Tuesday 3/21/23

Warm Up: 

Suppose you determine that the friction in one of your car's axles is contributing a torque of 0.05Nm.  If the axle is rotating through an angular distance of 72 radians, how much energy is lost due to this friction?  [Hint: how would you find energy loss due to friction if the motion were linear?]

Today: 

Homework:  

Class 56.75 Monday 3/20/23

Warm Up: 

None

Today: 

  • Assemble your rubber band car.  See videos from last class.  And here's a pdf that should be helpful -- Car assembly directions

    • Here's a photo showing where all the stuff is...

    • Parts are in the manila envelopes with one the name of one group member written in green ink near the top of the folder, where the car frame is likely to be sticking out.

    • Hot glue guns and glue sticks are on the counter.

    • Other supplies (axles, extra bushings, rubber bands, etc.) are in the box lid.

  • Do not actually wind up and drive the cars!  The whole point is to predict performance before you ever road test your car. 

  • You could start setting up your rubber band and string configuration.  Before that, you might want to measure the static force of friction of your drive wheels, so that you can see how much maximum rubber band force your car can handle without slipping.

Homework:  

  •  Think about how you are going to set up your bands and string.

Class 56.5 Friday 3/17/23

Warm Up: 

How can you measure the maximum force of static friction of your car's drive wheels?

Today: 

  • Check/review homework

  • Select your frame and wheel sizes -- we can do this together.

  • I won't be here on Monday.  On Monday you will be assembling your cars -- but you're not allowed to actually drive the cars by winding the string around the axle.  You could start measuring your moments of inertia, static friction, etc.

Homework:  

Class 56.25 Thursday 3/16/23

Warm Up: 

A single rubber band (labeled A in the diagram), stretched a distance x, has a tension of 1N.  How far must the other configurations (described below) be stretched in order to have that same tension of 1N? [Assume that the rubber bands behave like ideal springs with a constant k.]

B.  2 rubber bands, juxtaposed
C.  2 rubber bands, linked at the end
D. 1 rubber band, cut and arranged into a single strand

Today: 

  • Check/review homework

  • Work time

Homework:  

Class 56 Wednesday 3/15/23

Warm Up: 

1.  How can you find the North Star?

2.  Why won't this work in 3,000 years?

Today: 

Homework:  

Image result for quadcopter controlsClass 55.5 Tuesday 3/14/23

Warm Up: 

A quadcopter has four propellers that usually alternate in their directions of rotation.

  1.  How does conservation of angular momentum enable this quadcopter to achieve a yaw? 
  2.  In order to pitch or roll, why can't one motor just speed up (without the opposite motor slowing down)?

 

Today: 

  • Check/review homework

  • Problems

Homework:  

Class 55 Monday 3/13/23

Warm Up: 

  1.   How do falling cats always manage to land on their feet?
  2.   How can we simulate this?
  3.   Could we manage a linear version of this?

 

Today: 

Homework:  

Class 54.5 Friday 3/10/23

Warm Up:  The "tricky ones" from the lab were the calculations of I (for the wheel and axle) and the torque caused by friction.  To keep this simple, friction is assumed to be the same for both the acceleration and deceleration periods.

 

Find I and the torque due to friction.

 

Today: 

Homework:  

  • None

Class 54 Thursday 3/9/23

Warm Up: 

A sphere, a cylinder, a thin hoop, and a frictionless box are released from rest at the top of ramp.  Their masses and heights are identical.  Ignore air resistance (of course).

1.  Rank the objects according to their arrival times at the bottom of the ramp.

2.  Suppose the bottom end of the ramp is frictionless, and when they reach the bottom, the objects hit a vertical, frictionless wall.  What motions, if any, would continue after impact?

3.  How would the results be different if some objects had more mass or greater size than others?

4.  How would the results be different if the ramp itself were frictionless? 

Today: 

  • Notes: Rotational Kinetic Energy (p. 13) Notes Key
  • Finish and turn in the Practical Applications -- Find the moment of inertia of a wheel and axle (see assigment in Google Classroom).  Finish the "straightforward ones," and turn them in via Google Classroom.  If you worked in a group, just turn in one spreadsheet for your group.  Add a note including the group member names.  You can do the "tricky ones" later, or turn them in today for bonus points.
  •  
  • Consider this... given that we are assuming that friction is the same during acceleration and deceleration of the wheel and axle, are our determinations of moment of inertia too large or too small, or does this assumption have no effect on the direction of our error?
  • Work on the homework.

Homework:  

Class 53.5 Wednesday, 3/8/23

Warm Up:  Find the mass of the grey rod.  Assume that:

  • The rod, which is perfectly balanced horizontally, is supported entirely by the top string.
  • The rod's mass is evenly distributed along its length.
  • The strings' masses are negligible.

Today: 

  • Return retakes -- or give me your original test if you didn't leave it with me before break.
  • Finish the Practical Applications (from before break):
    • Find the moment of inertia of a wheel and axle (see assigment in Google Classroom).
      • Before you start the "tricky ones," turn-in a copy of your spreadsheet in Google Classroom.

Homework:  None

Class 53 Friday 2/24/23

Warm Up: 

None

Today: 

  • Optional test retake
  • Work on the Practical Applications (from last class):
    • Find the mass of a pipe using string, a ruler, the pipe, and one weight of known mass.  Prize for answers with 5% error or less = Fruit snacks!
    • Find the moment of inertia of a wheel and axle (see assigment in Google Classroom).
      • Before you start the "tricky ones," turn-in a copy of your spreadsheet in Google Classroom.

Homework:  None!

Class 52 Wednesday 2/22/23

Warm Up:  Consider the wheel and axle system on the right.  A string is wrapped around the axle, and a weight is tied to the string.  With the system initially at rest, the weight is released and begins to fall, unwinding the string and turning the wheels and axle. 

 

1.  How could you find the net torque that is being exerted on the axle?

2.  How could you find (approximate) the torque that is being exerted on the axle by friction?

Today: 

  • Review the homework
  • Chapter 10.3-10.4  Notes: Dynamics of Rotation (p. 11) Notes Key
  • Practical Applications (continue next class):
    • Find the mass of a pipe using string, a ruler, the pipe, and one weight of known mass.
    • Find the moment of inertia of a wheel and axle (see assigment in Google Classroom)

Homework:  

  • Due next class -- Dynamics of Rotation Practice (p.12) Practice Key

Class 51.5 Tuesday 2/21/23

Warm Up:  Suppose you need to screw an abutment into a fixture that is implanted in someone's jaw.  How can you make sure that you screw it in just tight enough, but not too tight?

Today: 

Homework: Chapt 10.2 -- Kinematics of Rotation Practice (p.10) -- Key

Class 51 Monday 2/20/23

Warm Up: 

In the rotational (angular) motion unit, we will be using new units that are analogous to our current, linear units.  You will need to be able to work in radians.

1.  360º = _____ radians

2.  90º = _____ radians

3.  2 radians = _____ degrees

 

Today: 

  • Return Tests
  • Retake on Friday.  You can choose to retake any of these parts of the test independently...
    • Short answer #1
    • Short answer #2
    • Short answer #3
    • Problems #1-3
    • Problem #4
    • Problem #5

Homework:  Angular Acceleration Practice (p. 8) -- Key

Class 50.5 Thursday 2/16/23

Warm Up: 

None

Today: 

  • Test

Homework: 

Class 50 Wednesday 2/15/23

Warm Up: 

Where does the fulcrum need to be placed in order to balance the beam?  The beam is 8m long.  It has an evenly distributed weight of 300N.

 

Today: 

  • Check/review homework
  • Test questions?
  • Formula list: 
  • The rest of the torque problems are due on

Homework: 

Class 50 Tuesday 2/14/23

Warm Up: 

Can you envision a collision during which...

1.    ...p is conserved, but mechanical energy is not?

2.    ...mechanical energy is conserved, but p is not?

3.    ...neither mechanical energy nor p is conserved?

4.    ...both mechanical energy and p are conserved?

 

If you know the impulse experienced by an object during a collision, what can you deduce about the object's...

5.   ...impact time?

6.   ...impact force?

7.  ...experience in general?

 

If you know the coefficient of restitution for an object's collision with another object, what can you deduce about the first object's...

8.   ...impulse?

9.   ...impact force?

10.   ...impact time?

11.   ...experience in general?

 

Today: 

Homework: 

Class 49.5 Monday 2/13/23

Warm Up: 

This Top Gear episode features a Renault Modus (compact car) vs. Volvo wagon in a head-on crash. 

1.  What will happen?

2.  Which is safer, a car that crumples in a crash or a car that is more rigid?

Today: 

  • Check/review homework
  • Short answer questions
  • The test has been moved to Thursday.

Homework: 

Class 49 Friday 2/10/23

Warm Up: 

Suppose I place some foam on my table top, and then I shoot it with the two darts in the picture, using the same Nerf ® gun.  Compare the effects of the two darts impact on the motion of the foam.

 

Today: 

  • Check/review homework.
  • Ballistic pendulum notes. 
  • Ballistic Pendulum Experiment -- what 1/2" PVC barrel length shoots a nerf dart fastest (when launched by 3L of air compressed to 40psi, and triggered by a sprinkler valve)?  Test (and make calculations for) one barrel at a time.
  • Test on Tuesday

Homework: 

  •  Complete the ballistic pendulum problem (#4) on p. 16. Solutions
  • If your understanding of the short answer practice test problems was fuzzy, read over my answers.  If you have any questions or continued fuzziness, email me and let me know.

Class 48.5 Thursday 2/9/23

Warm Up: 

1.  Consider a cart rolling down a ramp and colliding with a stationary block.  Describe how you could run four experimental trials that would demonstrate the combinations (1-4) of impulse (Ft) and coefficient of restitution (COR) shown in the table.  How would you set things up to achieve this outcome?

2.  Describe cart collisions (5-8) that would have the combinations of high and low impulse, impact force, and impact time, shown in the 2nd table.

Today: 

  • Return retakes
  • Check/review homework
  • Solving ballistic pendulum problems

Homework: 

  •  Practice test problems (p. 15-16, except for the ballistic pendulum problem) Solutions

Class 48 Wednesday 2/8/23

Warm Up: 

None

Today: 

  • Test retake (optional)

Homework: 

  •  Complete the multiple choice and short answer tarts of the pract test (p.13-16)...
    • p. 13 -- Multiple Choice:  Here are the answers...  
    •  p. 14-15 -- Short answer:  Here are some answers

Class 47.5 Tuesday 2/7/23

Warm Up: 

1.  What's interesting about a Newton's Cradle?

2.  What concepts does a Newton's Cradle demonstrate?

3.  What is the coefficient of restitution for a Newton's Cradle?

Today: 

  • Check/review homework
  • Check/review lab -- complete the lab quiz (score won't count) in Classroom.  See if answer key is correct.

Homework: 

  • Optional test retake tomorrows (energy and work)
  • Due on Thursday -- Complete the multiple choice and short answer tarts of the pract test (p.13-16)...
    • p. 13 -- Multiple Choice:  Here are the answers...  
    •  p. 14-15 -- Short answer:  Here are some answers

Class 47 Monday 2/6/23

Warm Up:  The coefficient of restitution is defined as e = separation speed / closing speed

1.  Write an equation for the coefficient of restitution for a ball that bounces to a height of hf when dropped from a height of hi.  e = ?

2.  Calculate the efficiency of this same bounce.  Efficiency = ?

3.  What is the relationship between efficiency and coefficient of restitution for a collision (where no mechanical energy is stored as PE)?

4.  Would this same relationship apply to a bouncing collision on a ramp?

Today: 

Homework: 

  • Optional test retake on Wednesday.
  • Problems 13-15 on packet p. 9-10.  Answers are at the bottom of page 10.

Class 46 Thursday 2/2/23

Warm Up: 

1.  What happens when I hold a tennis ball on top of a basketball and drop them to the floor together?

2.  Can you explain why this happens in terms of momentum?

 

Today: 

Homework: 

Class 45.5 Wednesday 2/1/23

Warm Up:  When the two blocks collide, they stick together.  What is the shared velocity of the two blocks after the collision?

Today: 

Homework: 

Class 45 Tuesday 1/31/23

Warm Up:  None

Today: 

  • Test

Homework: 

  • None

Class 44.5 Monday 1/30/23

Warm Up: 

1. How does a hydraulic lift facilitate work with a small input force and a large output force?  In general, how do hydraulics produce so much force?

2.  How do gears work in a car with a manual transmission?  gearbox-diagram.gif (825×585)How Manual Car Gears Work » Learn Driving Tips

 

Today: 

Homework: 

  • Test tomorrow.  Study

Class 44 Friday 1/27/23

Warm Up: 

1.  What is the point of having a variety of gears on a bicycle? (or a car, motorcycle, etc.)

2.  Mechanical advantage is the ratio of the force you would apply if you weren't using a machine to the force you apply when when using the machine.  A mechanical advantage of 2 means you only need half the force when you use the machine.  Estimate the  mechanical advantage of the bicycle (see picture) in its current gear.

3.  Explain in physicsy terms how this makes the bike more effective? 

 

Today: 

Homework: 

  • Complete the Energy Conservation Drill on p.16   Solutions 

Image result for compound bow drawn

Class 43.5 Thursday 1/26/23

Warm Up: 

1.  Where does a compound bow store most of its energy?

2.  What purpose(s) do the pulleys of a compound bow serve?

Today: 

Homework: 

  • Complete the rest of the problem section of Mr. Pennington's 2015-2016 Test -- p. 15 of the packet.  Solutions

Class 43 Wednesday 1/25/23

Warm Up: 

Suppose I hang a spring from the ceiling.  I then hook a 200g mass to the bottom end of the spring and let go.  The mass falls and bobs up and down until it finally comes to rest.  The spring's constant is k = 4N/m.

1.  What is the maximum distance that this spring gets stretched?

2.  How far is the spring stretched after the bobbing stops?

3.  What would a graph of PE, KE, and total E look like, for the entire bobbing period?

Today: 

Homework: 

  • Complete p14 of Mr. Pennington's 2015-2016 Test.  Solutions

Class 42.5 Tuesday 1/24/23

Warm Up: 

For an ideal spring, the applied force is directly proportional to the stretch distance.

The spring constant, k, is a ratio of force to stretch distance.  The units we will use for k are N/m. 

Suppose a screen door spring has a spring constant k = 40N/m.

1.  What is the tension in the spring when it is stretched 1m?

2.  What is the tension in the spring when it is stretched 20cm?

3.  How much work is required to stretch the spring from a stretch distance of 0m to a stretch distance of 1m?

*In the case of a compression spring, x is the compression distance.

Today: 

  •  Look at midterms
  • Course recommendations? Wildlife ecology?
  • Springs notes (packet page 7-8)  Notes key

Homework: 

Class 41.5 Friday 1/13/23

Warm Up:  None

Today:  Midterm Review

  • Question & Answer Session 
  • Jeopardy!

Homework: 

  • None.  Prepare for the midterm.

Class 41 Thursday 1/12/23

Warm Up:  None

Today: 

  • Midterm update (multiple choice question bank, partial credit, etc.)-- see Google Classroom
  • Question & Answer Session 
  • Brainstorm an "extra formula list?"
  • Jeopardy!

Homework: 

  • None.  Prepare for the midterm.

Image result for wedge mechanical advantageImage result for hockey stick fulcrumImage result for boat winchClass 40.5 Wednesday 1/11/23

Warm Up: 

The pictures on the right all show simple machines.  Simple machines allow the same work to be done with more convenient combinations of force and distance. 

1.  For each picture, identify the machine (s).

2.  For each machine, tell how the machine alters the distance over which force must be applied by the human using the machine.

3.  How does the machine alter the force that the human must apply?

4.  Which "machine" is fundamentally different? Why?  If you don't have a quick answer to this, move on to the other questions and come back to this one.

Today: 

Homework: 

  • None.  Prepare for the midterm.

Class 40 Tuesday 1/10/23

Warm Up:  None

 

Today: 

  • Optional test retake

Homework: 

  • Continued from yesterday... Mr. Pennington's multiple choice test questions (p.11-13)  Solutions
  • Prepare for the midterm.

 

Class 39.5 Monday 1/9/23

Warm Up: 

Assuming that all three bows are drawn to a distance of 0.5m...

1.  Which bow stores the most energy when it is drawn to this distance?

2.  Estimate the energy stored in each bow.

3.  Why is the compound bow curve so different?

Today: 

Homework: 

  • Mr. Pennington's multiple choice test questions (p.11-13)  Solutions

 

Class 39 Friday 1/6/23

Warm Up: 

A compact car (1,500kg) and a fully-loaded dump truck (36,000kg) are traveling at the same speed on level ground...

1.  Compare the distances that they will slide if they both lock up their wheels and skid to a stop.  Assume that their coefficients of friction are equal.

2.  Compare the distances that they will travel up a "runaway truck ramp" before coming to a stop. 

Today: 

Homework: 

Class 38.5 Thursday 1/5/23

Warm Up: 

1.  Can you guess what the "sisyphus train" does?

2.  How did it get that nickname?

Today: 

Homework: 

Class 38 Wednesday 1/4/23

Warm Up:  In this video, a driver attempts to traverse a large loop-the-loop.  In order to safely complete his mission, how many g's do you suppose the driver needs to tolerate?  Why? [I believe the height of the loop is around 13m.]

Today: 

Homework: 

  • Work and Energy Practice Problems #3-5  on p. 3-4 of the packet -- helpful video

  • Optional Bonus, due on or before the Unit 6 test -- for an extra 1 percent on the test, calculate the minimum number of gs a driver would need to tolerate in order for their car to maintain constant contact with a 10m radius loop the loop (and show your work!) -- assuming that the driver does not use the accelerator or the brakes once they enter the loop, and that no energy is lost (to friction,etc.) during the loop traverse.  To simplify matters, further assume that the centers of mass of the driver and the car are traveling in a 10m radius loop.

Class 37.5 Tuesday 1/3/23

Warm Up:  What will happen to kinetic energy, potential energy, thermal energy, and total energy of the skateboarder during a ride in the half pipe?  A) with zero friction  B) with a lot of friction

Today: 

  • Return tests -- Optional retake next Tuesday
  • Midterm Exam:
    • The midterm will cover Units 1-5 (through gravity and circlular motion).
    • I have provided clean copies of the old tests in Google Classroom.  I have also provided videos explaining all of the items on the tests.
    • Here is a midterm review document from last year that you might find useful -- "Algorithms" for solving physics problems
    • We will be doing some in-class review.
  • The rest of the year:
    • Finishing Mechanics
      • Work and energy,
      • Momentum and Impulse
      • Rotational Motion
    • Electricity
    • Sound and Waves
    • Optics
  • New Unit -- Work and Energy.  Unit 6 Handout (PDF)

Homework: